The inoculation process has been used in making cast iron for more than 60 years and usually consists of adding a silicon alloy containing calcium, magnesium, strontium, barium, cerium, aluminum or other active ingredients, singly or in combination, directly to the molten metal either prior to or during the casting operation. Of all the inoculating alloys those containing calcium are the most popular because calcium appears to be the most versatile active ingredient.
Alloys of calcium and silicon, especially calcium silicide and calcium bearing ferro silicon, are well known and have been in continued use as inoculating agents by those skilled in the art of making cast iron. Calcium silicide is an alloy containing approximately 30% calcium with silicon approximately 60% and the balance iron. Calcium bearing ferro silicon is an alloy usually containing 1/2% or up to about 2% of calcium with the balance being iron and silicon.
Other alloys have been used at various times, containing greater or lesser quantities of calcium, but these are not in general use for the specific purpose of inoculating or nucleating cast iron.
Calcium has a limited solubility in molten cast iron and tends to form copious quantities of refractory slag when added as a metal to molten cast iron. By the same token, when using calcium silicon containing usually about 20-35% calcium, it is not possible to get all calcium into solution and relatively large quantities of slag are formed. Such an alloy is wasteful of calcium, which increases the price of the alloy considerably. On the other hand, alloys such as calcium bearing ferro silicon do not allow sufficient calcium into the molten cast iron because this concentration of calcium is too low.